Control system



Feb. 28, 1933. H, 5, LA RO E 1,899,575-

CONTROL SYSTEM Original Filed July. 19, 1929 In ventor-1 WWW IE" I v r 7 i i a A r Harold B.La ROQUG,

. His Attdrne f Patented Feb. 28, 1933 UNITED STATES PATENT OFFICE HAROLD B. .LA -ROQUE, OF UPPER DARBY, PENNSYLVANIA, ASSIGNON TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

CONTROL SYSTEM Application filed July 19, 1929, Serial No. 379,556. Renewed May 19, 1982.

This invention relates to control systems, more particularly to control systems in which electric discharge devices are employed, and has for an object the provision of a simple and efiicient means for controlling the operation of the discharge devices.

" This invention is particularly advantageous in illumination control systems in which each of a plurality of groups of lamps is divided into a plurality of individual circuits and has for a further object the provision of a flexible and versatile illumination control system for varying the intensity of illumination of the lamps either individually in circuits, or

simultaneously in groups, together with means having a minimum of open switching for remotely controlling large groups of lamps consuming proportionately large blocks of power. A further object of this invention is the provision of a control system embodying certain improvements in the control system which is the invention of Allen E. Bailey, J 1:, described and broadly claimed in Application Serial No. 374,592, illumination control system, filed June 28, 1929, and as.-, signed to the same assignee as the assignee of the present invention.

In carrying my invention into effect in one form thereof, I provide an electrical device for supplying alternating potentials .to the grid and anode of the electric discharge device together with means in circuit with the electrical device for varying between predetermined limits the phaserelationship between the potentials applied to the grid and to the anode.

In illustrating my invention in one form thereof, I have shown it as embodied in an illumination control system particularly adapted for controlling the intensity of illumination of the lighting system of 'a theater, in which the aggregate of lamps are-divided into color groups, eachiof which is divided into sub-groups, the sub-groups in turn being di= vided into individual lamp circuits across which are connected one or more lamps.

For a better and more complete under standing of my invention, reference should now be made to the accompanying drawing, in which Fig. 1 is a diagrammatic representacircuits, such for example, as that represented in the drawing by thetwo conductors 10 across which are connected a plurality of lamps 11. The circuit 10 may be an individual circuit of any color group, for example, the red roup.

Alternating current is supplied to the amps 11' from any suitable single phase source of supply, such, for example, as the two lines 13+-14= to which the conductors 10 are connected, and which, as shown in the drawing, formone phase of a'three-phase supply line represented by the three conductors 12, 13, 14.

In a theater lighting system it is necessary that the intensity of illumination of the lamps be variable in various groups, and in combinations of groups and sub grou s, from full brilliance of the lamps to comp ete darkness thereof for the successful production of desired lighting effects for various scenes, such, by way of example, as sunrise, sunset, moonrise, and storm scenes;

In order to vary the intensity of illumination of an individual lamp circuit, a variable reactance having a soft iron core 15,

is provided with areactive winding 16 wound upon the core and connected in each individual lamp circuit in series relationship between the lamps 11 and their source of supply 13- 14. The core 15 is further provided with a saturating or controlwinding 17 which is connected in the output cir curt of a full wave rectifying device shown in the drawing as two elect ostatically controlled vapor-electric discharge devices 18 and 19 of the type known to the art by the term of thyratron. The thyratron is a three electrode tube difi'eringfrom the ordi-, nary three-element vacuum tube in that after exhaust a small quantity of inert gas, such for example, as mercury vapor, is introduced into the envelope, the .presence of which changes the pure electron discharge from the cathode, into an arc stream so that the thyratron becomes an electrostatically controlled arc rectifier. In the drawing, the tube 18 is provided with an anode 20, a grid 21, and a thermionic cathode or filament 22; tube 19 being provided with similar elements indicated respectively by the reference numerals 23, 24, 25 respectively.

The anodes 20, 23 of the thyratrons are connected to the opposite terminals of the secondary winding 26 of an anode transformer, the primary winding 27 of which is connected as by conductors 28, 29 to the terminals of the series connected legs 30 and 31 forming the secondary windings of a Scott or T-connected transformer, the significanceof which will'be made to appear more fully hereinafter in the description and explanation which follows. The filamentar'y cathodes 22, 25 of the tubes are heated by current supplied thereto from the termi nals of the secondary winding 32 of a filament transformer, the primary winding 33 of which is connected by conductors 29 to the terminals of the secondary windings 30-31 of the Scott-connected transformer.

As previously pointed out in this specification the control or saturating winding 17 of the variable reactance of the lamp circuit is connected in the output circuit of the full wave rectifying device comprising the tubes 18, 19. That is to say, one terminal of the winding-17 is connected to the midpoint of the secondary winding 26 of the anode transformer by a conductor 34, whilst its opposite terminal is connected by the conductor 35 to the midpoint of the secondary winding 32 of the filament transformer.

As is well understood by persons skilled in this art, the time of starting of the output current of a thyratron with respect to the beginning of each half cycle of the wave to be rectified can be controlled by the grid. After starting, the grid has no further control over the are, either to modulate, to limit, or to extinguish it; the instantaneous value of the magnitude of the current depending almost entirely upon the impedance of the external circuit. However, since the time of starting can be controlled in each half cycle, it is clear that the average value of the current in the output circuit can be controlled, and as a result of this contro in the particular connections shown in the drawing, the value of the current in the saturating winding 17 of the reactance. the value of the reactance itself, and likewise the value of the current flowing in the lamps 11 may be controlled. In order to provide adequate control of the phase relationship between the grid and anode potentials such as the control required in a theater lighting system, it is necemary to limit the angular displacement of these potentials, to the operating portion of the characteristics of the tube. To accomplish this result, I provide a grid phase control system in which the angular displacement of the grid potential with respect to the anode potential is limited to substantially 9O electrical degrees, 'i. e. from a position of substantial phase coincidence of these potentials to a position in which the grid potential lags the anode potential 90 electric degrees.

In this arrangement the grids 21 and 24 of the tubes 18, 19 are connected to opposite terminals of the secondary winding 37 of a grid transformer, the primary winding 38 of which is connected in series relationship with the secondary leg 31 of the Scott-connected transformer and either of the secondary windings 39, 40 of the grid phase-shifting transformers, the respective primary windings 41, 42 of which are supplied from the same phase 13-14 from which the primary leg 43 of the Scott-connected transformer is su plied.

cene changing contactors 44 and 45 are provided with windings 44a and 45a respectively, connected to be energized from the phase 1314 of the three-phase supply source in response to depression of either of the scene changing switches represented in the drawing as manually operated push buttons 46, 47 and serve to connect either of the secondary windings 39, 40 of the grid phaseshifting transformer in series with the primary winding 38 of the grid transformer and the secondary leg 31 of the Scott-connected transformer (depending upon which of the two scene changing contactors 44, 45 is ener gized and closed).

Although but a single pair of scene changing contactors 44 and 45 are shown in the drawing it is to be understood that there will be a similar pair for each individual lamp circuit in the entire system, as indicated by the open end conductors 44b, 45b, and that all of these contactors operate simultaneously in response to depression of the push buttons 46, 47, in the manner already described for the contactors 44, 45.

The grids of the tubes are biased slightly negatively by the biasing, or C battery 48, the negative terminal of which is connected through a current limiting resistor 49 to the midpoint of the secondary winding 37 of the grid transformer, and the positive terminal of the battery is connected by conductor 35 to the midpoint of the secondary winding 32 of the filament transformer. Current limiting resistors 50, 51 are also provided in'series relationship between the grids and the secondary of the grid transformer to prevent destruction of the grids. 1

The manner in which the phase of the potential applied to the grids is shifted with respect to the anode potential to control the saturating or control current flowing in the winding 17 of the reactor, will now be explained and will best be understood by referring to the vector diagram of Fig. 2 in which the voltage induced in the secondary legs 30, 31 of the Scott-connected transformer may berespectively represented by the two vectors AB and AD shown differing from each other in time phase by 90 electrical degrees, or in time quadrature,-as is well understood in the art. Since the primary 27 of the anode transformer is connected across the terminals of both legs 30, 31 of the Scott transformer, the voltage induced in the secondary 26 of the anode transformer will be the geometrical sum of the voltages of the legs and 31 and may be represented vectorially by the vector AC which is the resultant of the vectors AB and AD.

The voltage applied to the anodes 20 and 23 is represented therefore by the vector AC which la s AB and leads AD (assuming a counter c ockwise rotation of thevectors) by an angle of degrees. J

The voltage applied to the grids 21 and 24 is the sum of the voltage of one leg 31 of the Scott transformer represented by the vector AD and the voltage induced in the secondary winding 40 of the phase shifting transformer, (assuming scene change switch 44 to be closed), which when coil 40 is in the position shown is 90 electrical degrees out of phase with AD and may therefore be represented by the vector AF. The resultant AE of these two vectors represents the voltage applied to the grids, and as will be seen, it lags the vector AC of the anode voltage b 90 electrical degrees. The secondary win ing 40 of the grid phase shiftin transformer, however, is rotatably mounte upon a shaft 52 which is provided with a knob 53 by means of which the secondary coil '40 may be rotated in s ace 180 degrees from the position in which it is shown, thus causin the voltage AF induced therein tobe varie in magnitude and thereby to be shifted 180 electrical degrees from the position shown in Fig. 2 to a position of coincidence with AB which also effects arotation of the resultant vector AE (the grid potential) from the position shown through" 90 electrical degrees to .a position of coinc-i' dence withAC (the anode otential). Thus (f voltage AE may it will be clear that the gri be shifted. through the angle'C'*AE- .either from a position 90 degrees out of phase with. the anode voltage to coincidence therewith, or from a position of coincidence to a: osi-' tion 90 degrees out of phase-therewit "by rotation of the secondary coil gi the phase shifting transformer. v Persons skilled in the art will appreciate that when the gridand anode volta es are exactly in phase the average value of t e current in the output circuit will be maximum. and that this average value will decrease towards a minimum as the phase angle between the anode and the grid voltages becomes increased. In the connection shown, the output current will be a minimum when the grid voltage lags the anode voltage .90 degrees.

It is also to be notedthat a half complete .revolution of the coils 39,40 of the biasing transformers results in changing the magnitudes of the electromotive forces induced therein from 'a maximum positive value AF any number of revolutions of the coils 39, 40

of the biasing transformer can only result in repetition of the above operation. In

other words the phase angle between the grid and anode potentials is limited to the predetermined electrical angle GAE (Fig. 2). This limitation of the phase angle is an important feature since it prevents the increase of the phase angle to such a value (c. g. 180) that the electric discharge device becomes non-conducting over the entire cycle of anode potential. This feature is particularly important in a theatre lighting system of the type herein disclosed, since the current in the output circuit of the electric discharge device is always confined to the operating range of the device and the brilliancy of the controlled lamps is always at the value indicated by the position of the indicator 73 on the dial 74, irrespectively of any number ofrevolutions of the coils 39. 40 continuously in-the same direction. That is, the coils 39, 40 may be continuously rotated any num ber of revolutionsin the same direction without exceeding the operating range of the electric discharge device.

Although in the arrangement just described the displacement of the grid potential with respect to that of the anode is confined to 90 electrical degrees, I would have it understood that the invention is not limited thereto. since the angle of displacement may be varied at-will by varying the relative magnitudes of the potentials represented by i the vectors AD and AF as will be understood by persons skilled in this art.

From the foregoing it will be clear that the saturating current of the reactors (the output current of the tubes) will be minimum, the reactance maximum and the intensity of illumination of the lamps 11 minimum when the grid voltage is 90 degrees out of phase with the anode voltage; and that rotation of the coil 40 through one half turn will effect substantial coincidence of the grid and anode voltages, maximum saturating current of the control wlndmg of the reactor, minimum reactance-of the reactor, and

maximum intensity of illumination of the 1am s 11.

A though the lamp current will not be reduced to zero when the grid voltage of the thyratrons lags the anode voltage electrical degrees, it will nevertheless be diminished to such a value that the lamps will cease to be visible.

The individual circuits, such as the circuit 10, are so numerous in a theater illumination system that it is not possible to vary the intensity of illumination-of all the circuits simultaneously by the manually operated knobs 53. Remote control of many circuits in large groups and pre-setting of next scene circuits during the present scene becomes necessary.

In the system shown remote control is effected by remote motion transmitting devices connected to motion receiving devices which drive the shafts 52 upon which the secondary windings 39 and 40 of the gridphase shifting transformer are mounted.

A master motion transmitting device 54, known as a grand master, has a single phase rotor winding, the terminals of which are connected to asuitable single phase source, such for example, as the phase 13-14 of the three-phase supply line. This winding 1s mounted upon a shaft 55 in inductive relation to a distributed three circuits stator winding (not shown) and may be rotated with respect thereto by a knob 55a. An instrument of this type is on the market under the trade name Selsyn. scribed in U. S. Patent #1,612,119 E. M. Hewlett et al., dated Dec. 23, 1926.

' Intermediate motion transmitting devices 56, 57 58, known as color masters, are each provided with a distributed three circuit rotor winding and with a distributed three circ'uit stator winding, the terminals of which are connected to the three-phase stator winding of the grand master .54. Devices of this type are on the market under the trade name selsyn transformers, and are described in detail in U. S. Patent 1,612,117 E. M. Hewlett et al., dated Dec. 28, 1926. There are as many of these color masters connected to the grand master as there are color gr ups of lamps, i. e., the color master 56 may be for the red color gro'up, color master 57 for the blue color group, and color master 58 for the white group, with the necessary number of corresponding color masters for other color groups (not shown).

The control is further refined in that a plurality of group-masters 59, 60. 61 are connected to each of the color masters, those in the drawing being shown connected to the color master 56. There will be a corresponding plurality of group masters for each of Such an instrument is fully de-.

the remaining color masters 57, 58 as indicated by the open-end of the rotor windings of these color masters. The group masters are transmitting instruments similar in all respects to the color masters just described and their stator windings are connected to the rotor windings of their corresponding color masters.

The control is still further refined by a pl'urality of motion receiving instruments 62, one for each individual circuit 10 in the entire illumination system, connected to the rotor winding of its corresponding group master. The motion receiving instruments 62 are identical in construction with the transmitting device 54, i. e., the receiving devices 62 have single phase rotor windings connected to the same single phase source to which the rotor winding of the transmitting device 54 is connected, and they are also provided with distributed three circuit stator windings which are connected to the rotor windings of their corresponding group masters. It is clear that there will be as many of these receiving instruments in the system as there are individual lamp circuits 10 in the system.

The operation of the above described motion transmitting and receiving instruments is well understood in the art, and will be but briefly described in the present specification. When the rotors of the transmitting devices, the intermediate transmitting transformers, and the motion receiving devices are in their normal positions, the voltages induced in the three-circuit windings of the transmitting device will exactly balance voltages induced by the single-phase winding in the threecircuit windings of the motion receiving devices. Likewise the voltages supplied from the three-circuit windings of the transmitting device 54 to the three circuit windings of the transmitting transformers 56, 57, 58 will be exactly counter-balanced by the voltages supplied from the three circuit windings of the motion receiving devices to the three circuit rotor windings of the transmitting transformers. Should the single phase winding of the transmitting device 54 e rotated with respect to the stator winding, this voltage balance will be disturbed, and circulating currents will be set up through the three circuit windings all the way down through the selsyn transformers to the motion receiving devices, and in accordance with a well-known property of synchronous electrical machinery, the rotors of the receiving devices 62 which are free to rotate, will ass'ume a position to re-establish the balance, and the movement necessary to re-establish this balance will be exactly the same number of electrical degrees as that through which the rotor of'the transmitting device was displaced. Thus, it will be clear that any motion imparted to the rotor of the transmitting device will cause the rotors of the receiving devices 62 to follow this motion exactly. Gorrespondingly, if the rotor winding of any of the intermediate transmitting transformers 5 6, 57 58 is rotated with respect to its stator winding, arcorre-sponding unbalance of the currents flowing in its secondary winding and supplied from its secondary to all the motion receiving devices connected thereto, will result, and the rotors of the motion receiving devices will follow the motion of the rotor of this intermediate transmitting transformer to re-establish the balance. The same will be true if the rotors of any. of the intermediate transmitting transformers 59, 60, 61 are rotated.

The bearing systems of the transmitting device 54 and the intermediate transmitting devices, i. e. the transformers, are constructed to have sufficient drag or friction to prevent their being turned except by manual manipulation of the knobs on the shaft. The rotors of the receiving devices 62, however, turn freely. Thus it will be understood that rotation of the rotor of'the transmitting device 54 or of the transmitting transformers will only effect rotation of the rotors of the receiving devices 62 which are connected thereto but willonot effect rotation of the rotors of any other intermediate transmitting transformer or transmitting device to which it may be connected.

In order that the uni-directional movement of any transmitting device may be niade to effect either brightening or dimming the lamps, the shaft of each motion receiving device 62 is connected to the shaft upon which the rotors of the phase shiftingtransformers are mounted, through suitable reversing'gearing such as that shown in the drawing. The par-.

ticular reversing gearing shown is a magnetic gearing which consists of a soft iron disc 63 mounted upon a shaft 64 of each motion receiving device 62. A second soft iron disc 65 is connected through mechanical reversing gearing 66 to the shaft 64. Upon the shafts 52a, 52 upon which the rotor windings 39, 40 of the grid phase shifting transformers are respectively mounted, there are provided magnetic spools 67 68 engaging the soft iron disc 63, and magnetic spools 69, 7O engaging the soft iron disc 65. Each of the magnetic spools is provided with a coil, as shown, which may be energized from the phase 13- 55 14 of the three-phase supply line by operating e ther of the switches 7 1, 72, to either of its two operative positions. For instance, if direction switch 71 is operated to its left hand position, the cd'il for spool 68 will be energized, whereas if the switch is operated to its right hand position the coil for magnetic spool 70 will. be energized. Although not shown, the coils of these spools are supported so that they will remain fixed in space while permitting the spools to rotate. If the shaft spool 68, due to the magnetic attraction between it and the disc 63 will rotate exactly as if the spool and disc were two gears in mesh with each other. If the coil of spool is energized, motion will be imparted to the spool 70 by the rotation of s 001 65, and due to the reversing gearing 66 etween the shaft 64 and the disc 65, the direction of rotatfon of the spool 70 will be the opposite of that describedfor spool 68, and thus it will be clear that uni-directional motion of shaft 64 will effect opposite rotations of the secondary winding 40 of the grid phase shifting transformer, depending upon which of the two coils of the magnetic gearing is energized. The same is obviously true for the magnetic spools 67 and 69 which are connected-to the shaft 52a upon which secondary 39 is mounted.

With the above understanding of the various elements and controlling devices comprised in a system embodying my invention, the operation of the system itself will readily be grasped and'easily understood.

It will be clear from what has already been described of the operation of the system that manual operation of the knob'53 (assuming the scene change switch 44 to be operated to the closed position) will vary the intensity of illumination of lamps 11 connected across an individual circuit 10, either from full brilliancy to complete darkness, or from complete darkness to full brilliancy, by one half turn of the knob. If it be desired to vary the intensity of illumination of all of the lamp circuits in a sub-group simultaneously, this may be done by rotating the knob of one of the group masters. For example, by turning the knob of group-master 59, the rotors 'of'all of the motion receiving devices 62 connected liancy of all of the lamp circuits in that par= ticular sub-group. Should it be desired to .thereto will be rotated and will varythe brilvary the intensity of illumination of an en- 1 tire color group, this may be done by rotation of the knobs of one ofi the color masters. For

I example, assuming the color master 56 to be the red color master, the brilliancy of all of the red lamps in the theater may be simultaneouslyvaried by rotating the knob of this color master which will cause all of the mo tion receiving devices which are connected to all of the group masters associated with this particular color master, to rotate and to-vary thebrilliance of all the individual lamp circuits in this color group. Quite obviously, rotation of the knob of the grand master 54 will be eflective to vary the intensity of illumination of all the individual circuits in the system simultaneously.

Very often, it is necessary, for instance in the production of sunrise and sunset scenes, to cause the brilliance of certain of the circuits to decrease simultaneously with increasing brilliance of certain other circuits. This may easily be accomplished in my system as follows: Assume that all of the knobs 53 for all of the individual circuits of an entire color roup, for instance the red color group, have een pre-set dark, i. e. for maximum dimness, and that all of the knobs 53 of the individual circuits of the remaining color groups have been pre-set for maximum brilliance. Then by operating all of the switches 71 (or-72, as the case may be) for all of the individual circuits in the red color group to the right hand position for reverse rotation of the shafts 52 (or 52d), rotation of the knob of the grand master 56 will effect increasing intensity of illumination of .all the individual circuits of the red color group, and decreasing intensity of illumination of all the individual circuits of the remaining color groups.

It willbe appreciated by persons skilled in this art that various combinations can be worked by switching similar to that just described.

Pre-setting of the next scene may be accomplished by rotating the secondaries of the .phase shifting transformers 39 for the desired degree of brilliance of each individual lamp circuit, as indicated by the pointer 73, which cooperates with a suitably graduated scale 74, while the present scene is on. When the scene change is to be' made, the scene change switch 46, i. e. the present scene switch is operated to the open position thereb deenergizing and opening all of the scene-changng contactors 44 in the system, whilst the scene-change switch 47 is operated to the closed position, thereby energizing and operating all of the scene change contactors 45 to the closed position and connecting all of the secondaries 39 of all the grid phase-shifting transformers 'to the primaries 38 of their respective grid transformers for all of the individual circuits in the system. Thereafter the desired remote control of sub-groups, groups individually or groups in unison may be effected by manipulation of the group masters, color masters, or grand master as explained above.

Although in accordance with the provisions of the patent statutes I have disclosed and explained the best forms of the invention now known to me, I would have it understood that the invention is not limited to the exact formsillustrated, since modifications, alterations and equivalent arrangements will readi suggest themselves to persons skilled in the art'without departing from the true spirit of this invention or from the scope of the annexed claims.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. In a control system the combination with an electric discharge device provided least two dephased components of alternating voltage to one of said circuits and means movable to vary the magnitude of one of said components.

2. In a control system the combination with an electric discharge device provided with inputand output circuits, of a load circuit operatively associated with said output circuit, a source of alternating current supply, means connected with said source for supplying an alternating potential to said 'outputcircuit and at least two dephased components of electro-motive force to said input circuit, and means comprising a device having relatively movable winding elements for varying the magnitude of one of said com ponents.

3. A control system comprising in combination a load circuit, means comprising an.

electric discharge device provided with an input circuit and with an output circuit connected to said load circuit, a source of alternating current supply, connections between said source and said output circuit for supplying an alternatin potential to said output circuit, means inclu ing connections between said source and said input circuit for supplying at least two dephased components of alternating potential to said input circuit, and means including a manually operable device having two relatively movable winding elements for varying the magnitude of one of said components.

4. The combination with a variable impedance having a plurality of windings, of a load circuit connected in one of said windings, an electric discharge device provided with an output circuit connected in circuit with the other of said windings and also provided with.

vary the magnitude of one of said compo nents.

5. In a control system the combination 13 with a load circuit, a variable reactor provided with a control winding and with a winding connected to said load circuit, an electric discharge device having an anode, cathode, and a grid, connections between said control winding and said cathode and anode,

a source of alternating current supply, connections between said-source and' said anode for supplying an alternating potential to said anode, a control circuit connected with said source and with said input circuit including two winding elements for supplying at least two dephased components of alternating potentials to said input circuit, and means for rotating one of said winding elements to vary the magnitude of one of said components.

, 6. In a control system the combination.

- with an electric discharge device provided with an input circuit and an output circuit, a source of alternating current supply, electrical connections between said source and said output circuit, electrical connections between said source and said input circuit whereby a voltage is applied to said input circuit, means for applying a second voltage to said input circuit having a predetermined phase relation with the first voltage so that the resultant of said voltages is applied to said input circuit and means'for varying the magnitude and direction of one of said voltages so as to vary the phase relation between saidresultant voltageand the voltage of said output circuit.

7. In a control system, the combination with an electric discharge device provided -with an input circuit and an output circuit, a

source of alternating current supply, electrical connectlons between said source and said output c1rcu1t, electrical connections between i said source and said inputcircuit for applying a voltage to said input circuit, means for i applying a second voltage to said input cirapplying out of phase alternating potentials.

to said input and output circuits and means cuit having a predetermined phase relationship with said first voltage so that the resultant of said voltages is applied to said input circuit, and means rotatable to vary the magnitude and directionofone of said voltages so as to vary the phase relationship between said resultant voltage and the voltage applied to said output circuit.

8. In a control system, an electric discharge device provided with an input andwith an output circuit, a controlled device operatively associated with said output circuit, means for conn'ected'in circuit with said first mentioned means and continuously movable in one directlon to vary the phase relation between 'said input and output potentials to continuously vary the current flowing in said output circuit between preestablished limits.

9. In a control system the combination with an-electric discharge device provided wiplh an input circuit and with an output circ 't including a device to be controlled thereby,

- of means for supplying an alternating voltage to said output circuit, means for supply-' ing the resultant of two dephased voltages to said input circuit and means comprising a pair of relatively movable members for va-' ry-ing the magnitude of one of said two dephased voltages to vary the phase relationship between said output voltage and said resultant voltage.

10. In a control system the combination with an electric discharge device provided with an input circuit and with an output circuit, and a control device operatively associated with said output circuit, a source of alternating current, electrical connections between said source and said input circuit whereby a voltage is applied to said'input circuit, a winding included-in said connection, means for inducing a second voltage in said winding having a predetermined phase relationship to the voltage of said source, and means for varying the magnitude of said induced voltage so as to vary the phase relationship between the voltages of said input and said output circuits.

11. In a control system, the combination with an electric discharge device provided with an input circuit and with an output circuit including a .device to be controlled thereby, .of means including one leg of a Scott connected transformer for supplying an alternatin potential to said input circuit, means including both legs of said Scott connected transformer for supplying an alternating potential to said output circuit lag ing a device to be controlled, a three phase source of supply, a Scott transformer having its primary connected to said source, an elece tric circuit'including both secondary legs off said Scott transformer for supplying an alternating potential to said output circuit, a biasing transformer su plied from one phase of said source, a secons electrical circuit including one secondary eg of said Scott transformer and the secondary of said biasing,

' transformer for supplying aresultant voltage displaced by a definite electrical angle from said output potential, and means mounting the secondary of said biasing transformer for rotation with respect to its primary to provide for varying the phase relationship between said input and output potentials between pre-established limits. 4

13. In an illumination control system, a plurality of lamps, a variable reactor in circuit therewith for controlling the intensity of illumination of said lamps,ian electric discharge device provided with an input and" with an output circmt, electrical connections between said output circuit and said reactor, a Scott connected transformer having lts secondary wlndlngs connected in series relationship, connections between said secondary and I in the secondary of said biasing transformer to vary the phase relationship between said resultant voltage and the voltage supplied to said output circuit, thereby to control the current flowing in said output circuit.

14. In an illumination control system, the combination with a plurality of lamps, of a variable reactor having a winding in series with said lamps to control the intensity of illumination thereof, an electric discharge device provided with an input circuit and with an output circuit including a control winding in inductive relation with said first mentioned winding to vary the reactance thereof, a Scott connected transformer having seriesconnected secondary legs, connections between the terminals of said legs and said output circuit to apply the resultant of the voltages induced in said legs to said output circuit, a biasing transformer having its secondary connected in circuit with a leg of said Scott connected transformer and said input circuit to supply an alternating potential to said input circuit, and means for varying the magnitude of the voltage induced in the secondary of said biasing transformer to vary the phase relationship between the voltages supplied to said input and said output circuit.

15. In an illumination control system the combination with a plurality of lamps and a variable reactor having'a winding in circuit with said lamps to control the intensity of illumination thereof, a Scott connected transformer having its secondary legs connected series, a full wave rectifying devicev having an input circuit and an output circuit including a control winding for said reactor, connections from the terminals of said legs for applying the resultant of the voltages induced therein to said output circuit, a biasing transformer having its primary supplied with voltage in phase with the voltage of one of said legs, a circuit comprising thesecondary of said biasing transformer and one of said legs for supplying a. resultant voltage to said input circuit, and means for 'varymg the magnitude of the voltage induced in the secondary of said biasing transformer, thereby to vary the phase relationship between the voltages applied to said input circuit and to said output circuit.

16. In an illumination control system the combination with a lamp circuitincluding a variable reactor for controlling the intensity of illumintion thereof, of a full wave rectifying device providedwith an input circuit,

and with an output circuit including a-control winding for varying said reactor and means .for controlling said output circuit, said means including a Scott connected transformer having its secondary terminals connected to said output circuit for applying an alternating voltage thereto, a biasing transformer supplied with voltage in phase with the voltage of one of said legs, means including the secondary of said biasing transformer and the other of said legs for supplying the resultant of two component Voltages to said input circuit in phase with said output circuit voltage, and means for rotating the secondary of said biasing transformer to dephase said input potential from said output potential.

17. In an illumination control system, the combination with a lamp circuit includin a variable reactor for controlling the intensity of illumination thereof, of a full Wave rectifying device provided with an inputcircuit, and with an output circuit including a control winding for varying said reactor and means for controlling said output circuit said means including a Scott connected transformer having its secondary terminals connected to said output circuit for applying an alternating voltage thereto, a biasing transformer supplied with voltage in phase with the voltage of one of said legs, means including the secondary of said biasing transformer and the other of said legs for supplying the resultant of two component voltages to said input circuit, in phase with said output circuit voltage, and means for rotating the secondary of said biasing transformer-to dephase said input potential from said output potential, the proportion between said components being such that 18O degrees rotation of one of said components is effective to rotate. their resultant through an angle of less than 180 degrees.

18. In an illumination control system the combination with a lamp circuit including a variable reactor for controlling the intensity of illumination thereof, of a full wave rectifying device provided with an input circuit, and with an output circuit includng a control winding for varying said reactor and means for, controlling said output circuit and means including a Scott connected transformer having its secondary terminals condisplacement of the resultant thereof is limited to a predetermined angle.

19. In a control system the combination with an electric discharge device provided with an input circuit and an out ut circuit, a

source of alternatin current, e ectrical connections between sai source and said output circuit for applying a voltage to said output circuit, a circuit connected to said source and said input circuit for supplying a component voltage to said input circuit, a rotatably mounted. winding element included in said circuit, means for inducing a component voltage in said Winding varying in magnitude and direction with the angular position of said winding whereby the resultant of said component voltages is applied to said input circuit, and means for rotating said winding element to vary the phase relationship between said resultant voltage and the voltage of said output circuit.

In witness whereof, I have hereunto set my hand this 16th day of July, 1929.

as HAROLD B. LA ROQUE. 

